RINA - Démonstrateur d’utilisation de l’intelligence artificielle pour la gestion opérationnelle des risques naturels gravitaires géologiques | FEREC 2020

8 CHAPTER 1. RÉUNION ROCKFALL DATA ANALYSIS 7. TWI.csv ( Spatial ): a Topographic Wetness Index of the cliff top every 10 m date pr size 2008-12-06 9.45 3 2008-12-21 8.15 40 2008-12-29 12.8 5 2009-01-03 12.25 1.5 2009-01-03 12.35 1 ... ... ... (a) events.csv date rain ... ... 2008-12-19 2 2008-12-20 28 2008-12-21 8 2008-12-22 0 ... ... (b) rain.csv zone pr start pr end 0 1.7 2.9 2 2.9 3.1 0 3.1 5 ... ... ... (c) zone_geo.csv zone pr start pr end 0 1.7 2 1 2 5.3 0 5.3 5.5 ... ... ... (d) zone_protect.csv Table 1.1: Database related to Réunion Remarks: • Two or more rockfalls can occur the same day but at different position PR. • Protection and geological zone can be see as categorical function define for each PR of the road, i.e. f ( pr ) =type of zone. • Indexes standarized_area, SCI and TWI.csv are computed every 10 m from the cliff profile using a DEM model. Time, location and size are own characteristics of rockfall hazard. Rain, geological and protections, are external but can induce rockfall process. 1.2 Previous studies on rockfall and rainfall In the paper [3] , they look at rockfall hazard which is the probability that a rockfall of a given volume occurs in given area within a specified time interval. This definition is mathematically reflected by point process definition (see next chapter). They examine correlation between me- teorological factors and rockfall on 3 databases including RN1 in Réunion like us (Burgundy and Auvergne too). Their database is composed of 949 rockfalls events between 1998 and 2009. They highlights presence of correlation between rockfalls and rainfall and between rockfalls (and minimum temperatures for other sites). More precisely correlation is significant from 0 to 5 days. In the paper [2] , they study rockfall from the Mont Saint-Eynard (Grenoble) thanks to laser scan and photos at different time frequencies. Their database count 1068 rockfall events acquired from photos and a laser scan. Two external factors are well studied : rainfall and freeze-thaw cycle. As negative temperature does not occur in Réunion, we just mention here results about rainfall. Adding to rainfall times series, they used rainfall episode . A rainfall episode begins when it rains back after a given delay without rain. This time delay is set in order that 2 rainfalls episodes are independent, i.e. the effect of first one stop before the second one begins. Such delay on the